Carcinoma of the cervix: deficiency of nexus intercellular junctions

Multi-omics analysis of expression profile and prognostic values of connexin family in LUAD

PURPOSE

Our study first explored the expression differences and prognostic significance of Cx genes in pan-cancer and then focused on LUAD. Our objectives were to conducted a comprehensive analysis of the expression profile, prognostic significance, genetic alterations, potential biological functions and drug sensitivity of the Connexin gene family in LUAD.

METHODS

We developed a comprehensive prognostic model for LUAD by combining risk scores with clinical features and created a nomogram to predict 1-, 3-, and 5-year overall survival. Using single-cell sequencing, we examined the expression and biological functions of the identified prognostic markers.

RESULTS

Our risk model revealed that GJB2-5 play a critical role in the prognosis of LUAD patients, associated with many biological processes such as cell cycle, DNA damage, EMT, hypoxia, invasion, and metastasis. Furthermore, the connexin gene family is linked to transcriptional mechanisms such as the extracellular matrix (ECM), migration, mobility, angiogenesis, and the epithelial-mesenchymal transition (EMT) genetic program.

CONCLUSION

The risk model can be used as a potential prognostic factor for LUAD patients and may provide new insights into cancer treatment from perspective of the expression of Cx genes.

Reprogramming of connexin landscape fosters fast gap junction intercellular communication in human papillomavirus-infected epithelia

Human papillomaviruses (HPVs) are highly prevalent commensal viruses that require epithelial stratification to complete their replicative cycle. While HPV infections are most often asymptomatic, certain HPV types can cause lesions, that are usually benign. In rare cases, these infections may progress to non-replicative viral cycles associated with high HPV oncogene expression promoting cell transformation, and eventually cancer when not cleared by host responses. While the consequences of HPV-induced transformation on keratinocytes have been extensively explored, the impact of viral replication on epithelial homeostasis remains largely unexplored. Gap junction intercellular communication (GJIC) is critical for stratified epithelium integrity and function. This process is ensured by a family of proteins named connexins (Cxs), including 8 isoforms that are expressed in stratified squamous epithelia. GJIC was reported to be impaired in HPV-transformed cells, which was attributed to the decreased expression of the Cx43 isoform. However, it remains unknown whether and how HPV replication might impact on the expression of Cx isoforms and GJIC in stratified squamous epithelia. To address this question, we have used 3D-epithelial cell cultures (3D-EpCs), the only model supporting the productive HPV life cycle. We report a transcriptional downregulation of most epithelial Cx isoforms except Cx45 in HPV-replicating epithelia. At the protein level, HPV replication results in a reduction of Cx43 expression while that of Cx45 increases and displays a topological shift toward the cell membrane. To quantify GJIC, we pioneered quantitative gap-fluorescence loss in photobleaching (FLIP) assay in 3D-EpCs, which allowed us to show that the reprogramming of Cx landscape in response to HPV replication translates into accelerated GJIC in living epithelia. Supporting the pathophysiological relevance of our observations, the HPV-associated Cx43 and Cx45 expression pattern was confirmed in human cervical biopsies harboring HPV. In conclusion, the reprogramming of Cx expression and distribution in HPV-replicating epithelia fosters accelerated GJIC, which may participate in epithelial homeostasis and host immunosurveillance.

Direct Intercellular Communications and Cancer: A Snapshot of the Biological Roles of Connexins in Prostate Cancer

Tissue homeostasis is the result of a complex intercellular network controlling the behavior of every cell for the survival of the whole organism. In mammalian tissues, cells do communicate via diverse long- and short-range communication mechanisms. While long-range communication involves hormones through blood circulation and neural transmission, short-range communication mechanisms include either paracrine diffusible factors or direct interactions (e.g., gap junctions, intercellular bridges and tunneling nanotubes) or a mixture of both (e.g., exosomes). Tumor growth represents an alteration of tissue homeostasis and could be the consequence of intercellular network disruption. In this network, direct short-range intercellular communication seems to be particularly involved. The first type of these intercellular communications thought to be involved in cancer progression were gap junctions and their protein subunits, the connexins. From these studies came the general assumption that global decreased connexin expression is correlated to tumor progression and increased cell proliferation. However, this assumption appeared more complicated by the fact that connexins may act also as pro-tumorigenic. Then, the concept that direct intercellular communication could be involved in cancer has been expanded to include new forms of intercellular communication such as tunneling nanotubes (TNTs) and exosomes. TNTs are intercellular bridges that allow free exchange of small molecules or even mitochondria depending on the presence of gap junctions. The majority of current research shows that such exchanges promote cancer progression by increasing resistance to hypoxia and chemotherapy. If exosomes are also involved in these mechanisms, more studies are needed to understand their precise role. Prostate cancer (PCa) represents a type of malignancy with one of the highest incidence rates worldwide. The precise role of these types of direct short-range intercellular communication has been considered in the progression of PCa. However, even though data are in favor of connexins playing a key role in PCa progression, a clear understanding of the role of TNTs and exosomes is needed to define their precise role in this malignancy. This review article summarizes the current view of the main mechanisms involved in short-range intercellular communication and their implications in cancer and delves into the biological, predictive and therapeutic role of connexins in PCa.

Connexins in cancer: bridging the gap to the clinic

Gap junctions comprise arrays of intercellular channels formed by connexin proteins and provide for the direct communication between adjacent cells. This type of intercellular communication permits the coordination of cellular activities and plays key roles in the control of cell growth and differentiation and in the maintenance of tissue homoeostasis. After more than 50 years, deciphering the links among connexins, gap junctions and cancer, researchers are now beginning to translate this knowledge to the clinic. The emergence of new strategies for connexin targeting, combined with an improved understanding of the molecular bases underlying the dysregulation of connexins during cancer development, offers novel opportunities for clinical applications. However, different connexin isoforms have diverse channel-dependent and -independent functions that are tissue and stage specific. This can elicit both pro- and anti-tumorigenic effects that engender significant challenges in the path towards personalised medicine. Here, we review the current understanding of the role of connexins and gap junctions in cancer, with particular focus on the recent progress made in determining their prognostic and therapeutic potential.

Facets of Communication: Gap Junction Ultrastructure and Function in Cancer Stem Cells and Tumor Cells

Gap junction proteins are expressed in cancer stem cells and non-stem cancer cells of many tumors. As the morphology and assembly of gap junction channels are crucial for their function in intercellular communication, one focus of our review is to outline the data on gap junction plaque morphology available for cancer cells. Electron microscopic studies and freeze-fracture analyses on gap junction ultrastructure in cancer are summarized. As the presence of gap junctions is relevant in solid tumors, we exemplarily outline their role in glioblastomas and in breast cancer. These were also shown to contain cancer stem cells, which are an essential cause of tumor onset and of tumor transmission into metastases. For these processes, gap junctional communication was shown to be important and thus we summarize, how the expression of gap junction proteins and the resulting communication between cancer stem cells and their surrounding cells contributes to the dissemination of cancer stem cells via blood or lymphatic vessels. Based on their importance for tumors and metastases, future cancer-specific therapies are expected to address gap junction proteins. In turn, gap junctions also seem to contribute to the unattainability of cancer stem cells by certain treatments and might thus contribute to therapeutic resistance.

On being a pathologist: a pathway to pathology practice; the added value of supplemental vocational training and mentoring in college and medical school

Traditionally, vocational training and liberal arts (and premedical) curricula have been separate education tracks. This personal profile describes a program that evolved from the partial fusion of vocational training and a premedical education track. My personal health issue, visual impairment, which presumably resulted as a complication of congenital toxoplasmosis, hampered my ability to read in grammar school and necessitated my placement in remedial reading classes until eighth grade. My father created an independent home-based vocational training program that ran in parallel to my traditional school education all the way through college. In this case study, I provide an overview of this hybrid education program, which we refer to as the Vocational Training/Medical College Curriculum of the Future (VTMC). This term implies that the education of a student from K-12 school through medical college is a continuum. I find it useful to conceptualize a single education continuum beginning with vocational training and ending with medical education, with a large overlap area in the middle. In this paper, I describe a set of my work experiences that leveraged and reinforced my didactic education experiences. Mentors who supported aspects of the VTMC program have included a college president, a US Congressman, a Nobel Laureate, and a Massachusetts General Hospital leader in academic pathology. Elements of this innovative VTMC program have been used in K-12 public schools and in nonmedical graduate school programs.

Gap junctions and cancer: communicating for 50 years

Fifty years ago, tumour cells were found to lack electrical coupling, leading to the hypothesis that loss of direct intercellular communication is commonly associated with cancer onset and progression. Subsequent studies linked this phenomenon to gap junctions composed of connexin proteins. Although many studies support the notion that connexins are tumour suppressors, recent evidence suggests that, in some tumour types, they may facilitate specific stages of tumour progression through both junctional and non-junctional signalling pathways. This Timeline article highlights the milestones connecting gap junctions to cancer, and underscores important unanswered questions, controversies and therapeutic opportunities in the field.

Connexins: junctional and non-junctional modulators of proliferation

Mounting evidence indicates that dysregulation of gap junctions and their structural subunits-connexins-often occurs in, and sometimes causes, a variety of proliferative disorders, including cancer. Connexin-mediated regulation of cell proliferation is complex and may involve modulation of gap junction intercellular communication (GJIC), hemichannel signalling, or gap junction-independent paths. However, the exact mechanisms linking connexins to proliferation remain poorly defined and a number of contradictory studies report both pro- and anti-proliferative effects, effects that often depend on the cell or tissue type or the microenvironment. The present review covers junctional and non-junctional regulation of proliferation by connexins, with a particular emphasis on their association with cancer.

Mechanistic basis of desmosome-targeted diseases

Desmosomes are dynamic junctions between cells that maintain the structural integrity of skin and heart tissues by withstanding shear forces. Mutations in component genes cause life-threatening conditions including arrhythmogenic right ventricular cardiomyopathy, and desmosomal proteins are targeted by pathogenic autoantibodies in skin blistering diseases such as pemphigus. Here, we review a set of newly discovered pathogenic alterations and discuss the structural repercussions of debilitating mutations on desmosomal proteins. The architectures of native desmosomal assemblies have been visualized by cryo-electron microscopy and cryo-electron tomography, and the network of protein domain interactions is becoming apparent. Plakophilin and desmoplakin mutations have been discovered to alter binding interfaces, structures, and stabilities of folded domains that have been resolved by X-ray crystallography and NMR spectroscopy. The flexibility within desmoplakin has been revealed by small-angle X-ray scattering and fluorescence assays, explaining how mechanical stresses are accommodated. These studies have shown that the structural and functional consequences of desmosomal mutations can now begin to be understood at multiple levels of spatial and temporal resolution. This review discusses the recent structural insights and raises the possibility of using modeling for mechanism-based diagnosis of how deleterious mutations alter the integrity of solid tissues.

Cell junctions and the biological behaviour of cancer

Quantitative and qualitative abnormalities in intercellular junctions have been described in a broad spectrum of human and animal cancers. Current efforts are aimed at exploring the possibility that some of these defects may account for the hallmarks of malignancy, namely tumour invasion and metastasis. This approach is hampered by a paucity of information on the natural history of human cancer. There is evidence from quantitative electron microscopy studies of urinary bladder carcinomas induced by a chemical carcinogen in Fischer rats that decreased intercellular adhesion, mediated in part by intercellular junctions, does not contribute to the invasive potential of tumours. However, it may account for increased cell shedding at the tumour surface. The increased leakiness of malignant epithelium is attributed to defects in occludens junctions. The defects appear to represent a failure to assemble intramembrane fibrils into fully competent occludens junctions, rather than a blockage of fibril synthesis. Gap junctional deficiencies are not an invariant in cancers. Further, gap junctional deficiencies are present in human cervical carcinoma-in-situ. These deficiencies are present many hundreds of cell generations before the development of invasive tumours. This argues against the hypothesis that gap junctions per se contribute to the biological behaviour (i.e. invasion) of malignant tumours.

Reduced expression of multiple gap junction proteins is a feature of cervical dysplasia

Cervical dysplasia is a premalignant lesion associated with human papillomavirus (HPV) infection which, over time, can turn cancerous. Previous studies have indicated that loss of gap junctions may be a feature of cervical cancer and premalignant dysplasia. Loss of the gap junction protein connexin43 has been demonstrated in dysplastic cervix, but other connexins have not been investigated. In contrast we previously showed that HPV-associated cutaneous warts – and other hyperproliferative skin conditions – display a dramatic upregulation of certain connexins, in particular connexin26. By performing immunofluorescence staining after antigen retrieval of paraffin-embedded cervical tissue samples, this study reports for the first time that connexin26 and connexin30, in addition to connexin43, are expressed in differentiating cells of normal human cervical epithelia. Moreover, in dysplastic ectocervix, all connexins studied display a dramatic loss of expression compared to adjacent normal epithelia. The role of connexins in keratinocyte differentiation and carcinogenesis is discussed.

The relationship between connexins, gap junctions, tissue architecture and tumour invasion, as studied in a novel in vitro model of HPV-16-associated cervical cancer progression

Disruption of gap junctional intercellular communication (GJIC) and/or connexins (gap junction proteins) is frequently reported in malignant cell lines and tumours. Certain human papillomaviruses (HPV) associated with the development of cancers, especially of the cervix, have previously been reported to downregulate GJIC in vitro. There is also evidence for reduced gap junctions in cervical dysplasia. However, many squamous hyperproliferative conditions, including HPV-induced warts, often show extensive upregulation of certain connexins. The association between HPV and GJIC, and the mechanism and consequence of deregulated GJIC in cervical tumour progression, remains unclear. Therefore, using a variety of nonmalignant and malignant cell lines and an organotypic raft-culture system, we investigated the relationship between HPV, gap junctions and tumour progression. Established cervical tumour cell lines carrying HPV were unable to communicate via gap junctions (when assayed by dye-transfer techniques). This correlated with lack of connexin protein expression, while transfection with connexins 26 or 43 led to functional gap junction membrane plaques. On the other hand, immortal but nonmalignant cell lines that contained episomal or integrated HPV-16, but required feeder-layer and growth-factor support, were consistently well coupled, and expressed multiple connexins at membrane junctions. In vitro selection of feeder-layer and growth-factor-independent variants eventually lead to loss of GJIC, which correlated with loss of membrane and increased cytoplasmic connexin 43 localization. However, this was preceded by loss of differentiation and stromal invasion, as assayed on the organotypic raft-culture model. Using this model, a comparison between noncoupled, well-coupled and connexin-transfected cell lines revealed no firm correlation between GJIC and dysplasia, but GJIC appeared to favour increased stratification. These findings demonstrate that loss of GJIC is frequent, but appears to occur more as a consequence of, rather than being the cause of, epithelial dysplasia, and may be influenced by, but is not directly attributable to, HPV.

Cell culture assays for chemicals with tumor-promoting or tumor-inhibiting activity based on the modulation of intercellular communication

The ability of chemicals with tumor-promoting or tumor-inhibiting activity to modulate gap junctional intercellular communication is reviewed. The two most extensively used types of assays for screening tests are (1) metabolic cooperation assays involving exchange between cells of precursors of nucleic acid synthesis and (2) dye-transfer assays that measure exchange of fluorescent dye from loaded cells to adjacent cells. About 300 substances of different biological activities have been studied using various assays. For tumor promoters/epigenetic carcinogens, metabolic cooperation assays have a sensitivity of 62% and dye-transfer assays 60%. Thirty percent of DNA-reactive carcinogens also possess the ability to uncouple cells. The complete estimation of the predictive power of these assays could not be made because the majority of the substances studied for intercellular communication effects in vitro have not yet been studied for promoting activity in vivo. Both metabolic cooperation assays and dye transfer assays respond well to the following classes of substances: phorbol esters, organochlorine pesticides, polybrominated biphenyls, promoters for urinary bladder, some biological toxins, peroxisome proliferators, and some complex mixtures. Results of in vitro assays for such tumor promoters/nongenotoxic carcinogens, such as some bile acids, some peroxides, alkanes, some hormones, mineral dusts, ascorbic acid, okadaic acid, and benz(e)pyrene, do not correlate with the data of in vivo two-stage or complete carcinogenesis. Enhancement of intercellular communication was found for 18 chemicals. Among these, cAMP, retinoids, and carotenoids have demonstrated inhibition of carcinogenesis. We examine a number of factors that are important for routine screening, including the requirement for biotransformation for some agents to exert effects on gap junctions. We also discuss the mechanisms of tumor promoter and tumor inhibitor effects on gap junctional permeability, including influences of protein kinase activation, changes in proton and Ca2+ intracellular concentrations, and effects of oxy radical production.

Dibutyryl cyclic AMP modulation of gap junctions in SW-13 human adrenal cortical tumor cells

Cultured human adrenal cortical adenocarcinoma cells (SW-13) form a confluent monolayer of epithelial-like cells when seeded into culture flasks. Following a 24-48 hr non-mitotic period, cells begin to divide and become confluent within a week after seeding at 5 X 10(4) cells/cm2. The SW-13 cells were exposed to dibutyryl cyclic AMP (DbcAMP), cyclic AMP (cAMP), sodium butyrate, and adrenocorticotropin (ACTH). The rate of SW-13 cell proliferation was measured with a DNA microfluorometric assay, as well as by procedures measuring the incorporation of 3H-thymidine. In addition, following administration of ACTH and DbcAMP, the fractional area of membrane covered by gap junctions was quantitated with freeze-fracture electron microscopic techniques. Dibutyryl cyclic AMP at a concentration of 1 X 10(-3) M decreased the growth rate of the cell population. There was a corresponding increase in the fractional area of gap junctions found on the cell membrane in 96-hr DbcAMP-treated cultures. ACTH (40 mU/ml) exposure failed to produce an increase in the fractional area of gap junctions or to alter the rate of cell proliferation. From these data it can be suggested that elevations in cAMP levels within the cell can be related to both the proliferation of gap junctions and the decrease in cell proliferation in the SW-13 tumor cell.

Cellular junctions in a spectrum of human malignant tumors

Cellular junctions in tumors are often considered a hallmark of epithelial differentiation. However, junctions are also seen in tumors having a different differentiation. This observation prompted us to study cellular junctions in malignant nonepithelial tumors. We found a variety of cellular junctions in such tumors, although the majority were poorly formed. This observation is of importance for diagnostic purposes. We have also tried to clarify the nomenclature of cellular junctions as applied in tumor diagnosis by proposing a systematic categorization of terms in everyday use by pathologists and by referring more extensively to the term paired subplasmalemmal densities (PSD) for non-well-formed junctions.

Intercellular contacts in tumours of the vascular smooth muscle cells in man

Electron microscopy has been used to study the cell to cell and cell to stroma contacts between smooth muscle cells (SMC) in normal vessels, angiomyolipoma and well and poorly differentiated vascular leiomyosarcoma. Micrographs were examined with a semiautomatic image analysis system. The length of the cell borders was calculated and the type and number of contacts per 100 micron cell perimeter and per 100 cells were determined. In all cases there was a predominance of simple appositions. Intermediate junctions, nexus junctions, interdigitations, intermediate contacts and junctional interdigitations were less frequently observed. In general, as the SMC become malignant and less differentiated the number of cell to stroma attachments decreases markedly and the intercellular contacts increase slightly.

Modification of gap junctions in cells transformed by a temperature-sensitive mutant of Rous sarcoma virus

Prompted by our observation that a reduction in junctional permeance is one of the earlier events in the process of neoplastic transformation of a cell line by Rous sarcoma virus, we analyzed the gap junctions from these cells to determine if the basis of the reduction is a loss of junctional channels. The cells (normal rat kidney, or NRK) are infected with a temperature-sensitive mutant of Rous sarcoma virus, allowing one easily to manipulate the cells into and out of the transformed state, and hence also to manipulate the junctional permeance. Using freeze-fracture electron microscopy, we found that the number and size of the junctions did not change in parallel with the permeance changes we had previously characterized. There is, however, a significant rearrangement of the junctional particles to a more random configuration when the cells are transformed and a reversal to the more ordered pattern when the cells are shifted back to the normal phenotype. These changes do parallel the changes in junctional permeance. We conclude that the permeance of existing junctional channels is modified and that the change in permeance may involve a change in the interaction of the junctional channels with each other and/or the surrounding lipid domain.

Changes occurring in plasma membranes and intercellular junctions during the process of carcinogenesis and in squamous cell carcinoma

A 0.5% mineral-oil solution of 9.10-dimethyl-1.2-benzanthracene (DMBA) was applied to artificial cecal pouches in the lower lips of rats. Ultrastructural studies were made of plasma membranes and intercellular junctions during the process of malignant transformation in the oral mucosal epithelium and after squamous cell carcinoma had been induced by the carcinogen. After the administration of DMBA, the inner leaflet of the membranes where the microfilaments are attached showed high electron density and intramembranous particles on the P-face of basal cells decreased to about half that of controls. However, on the E-face the number of intramembranous particles increased by approximately 10% compared with controls. Though the normal size range for intramembranous particles was 9-12 nm, the administration of DMBA caused aggregations of from three to six particles on the P-face. In squamous cell carcinomas, only the outer leaflet of the membranes showed high electron density; the number of intramembranous particles was 30% higher on the P-face and approximately three times higher on the E-face compared with controls and the morphology of the intramembranous particles, which formed irregular aggregates of from five to 20 particles, was specific. In animals treated with DMBA, the number of gap junctions decreased by between 50% and 70%, although no structural changes occurred. In squamous cell carcinomas, the area of gap junctions was about 50% lower and the number of gap junctions about 40% lower than in controls. Changes in the number and area of desmosomes were similar to those of gap junctions both in the DMBA-treated animals and in squamous cell carcinomas.

Glassy cell carcinoma of the uterine cervix. A light and electron microscopic study of five cases

Five cases of glassy cell carcinoma of the uterine cervix were examined by light and electron microscopy. Light microscopic features included areas of large cells with ground glass and granular cytoplasm, distinct borders, prominent stromal inflammation, and lack of apparent squamous or glandular differentiation. Two neoplasms were associated with separate foci of squamous cell carcinoma in situ and one with endocervical adenocarcinoma. Electron microscopy showed a predominant cell type with cytoplasmic filaments, dilated rough endoplasmic reticulum, Golgi complexes, and large nuclei with complex nucleoli. In some cells there were tonofibrils and well developed desmosomes. The neoplasm of one patient showed poorly developed intracellular lumina. These observations were interpreted to indicate that glassy cell carcinoma is associated with and demonstrates both glandular and squamous differentiation. It is, therefore, properly classified as a type of poorly differentiated adenosquamous carcinoma, which likely develops from the subcylindric reserve cell. The results of this experience reaffirms its poor prognosis.

Tumor invasion and host extracellular matrix

In this review some of the major mechanistic pathways by which tumor cells are thought to invade host tissues are discussed. Tumor invasion has been conceived to be the result of pathological, close-range interactions between malignant cells and host stroma. The sequence of events that characterize invasion can be summarized as follows: (a) Tumor cell clusters break from the confinement of the primary tumor. Loss of intercellular junctions (desmosomes), alterations in the chemical composition and physical properties of the cell surface coat (loss of fibronectin and heparan sulfate; excessive amounts of hyaluronate), and loosening of cell-substrate interactions (loss of hemidesmosomes, fibronectin, and heparan sulfate), are among the most frequently listed causes of tumor cell shedding. (b) Increased proteolytic activities at the invasion front cause focal alterations in the surrounding extracellular matrix, thereby changing its physical properties. Collagenases and cathepsins, as well as elastase and other neutral proteinases are the enzymes most frequently associated with matrix destruction and invasion. In some tissues this process is effectively regulated by inhibitors of matrix-degrading, proteolytic enzymes. (c) Tumor cells migrate into the altered matrix, possibly moving as aggregates along guidance tracks provided by host structures (blood vessels, lymphatics, nerves) or matrix macromolecules (collagen and fibronectin tracks). Migration seems to be preceded by increased swelling of glycosaminoglycan (i.e., hyaluronate) in the matrix, ahead of the migrating cell population. Various host cell types (mast cells, fibroblasts, endothelial cells, macrophages, etc.) may participate in these events.

Measurement of number and cross-sectional area of basal cell pseudopodia: a new morphometric method

A method of morphometric quantitative of the number of pseudopodia per individual basal cell and the ratio of the total cross-sectional area of the pseudopodia to the base area of the basal cell, using the transmission electron microscope, was developed. The diameters and areas of the bases of basal cells and the pseudopodia were also obtained. The number of pseudopodia per basal cell (N) and the ratio of the areas (F) measured in normal human uterine cervical epithelium were 34.22 and 0.338, respectively. The values observed in reactive atypia were 23.62 and 0.188; and those in mild dysplasia of the cervical epithelium (the earliest premalignant condition of the cervical epithelium), 26.98 and 0.226. There were statistically significant reductions in the number of pseudopodia per cell (N) and the ratio of areas (F) in the latter two pathological conditions compared to the controls. This morphometric method provides higher sensitive means by which one can quantify the characteristics of pseudopodia in various premalignant epithelia.

Direct intercellular communication in health and disease: an overview

Direct intercellular communication (cell to cell coupling) is a mechanism for the local transit of information between cells and supplements the endocrine and nervous systems. Electrophysiological, biochemical, histological and cell culture techniques have established the widespread existence of coupling in mammalian tissues, and the importance of the gap junction has been recognised. Information is carried in the form of ions and small molecules between cells, and sensitive apparatus exists within each cell for controlling the permeability of the junctional membrane. The system may be important in the control and co-ordination of cellular metabolism and growth in the embryo and in adult tissues. Disorders of direct intercellular communication may be important in the pathogenesis of some diseases, in particular cancer.

Influence of topical and systemic retinoids on basal cell carcinoma cell membranes

Although much recent work suggests that retinoids can prevent the development of epithelial cancers, their mechanism of action remains unknown. Since malignancy has been associated with alterations in gap junctions, desmosomes, microfilaments, and hemidesmosomes, the authors examined freeze-fracture replicas and thin sections of cell membranes of: (1) 11 basal cell cancers (BCC) treated twice daily for two weeks with topical 1.0% retinoid acid (RA); (2) 21 BCC treated for 2 to 17 weeks with oral 13-cis retinoic acid (CRA) (1.0-8.0 mg/kg/day); and (3) 17 BCC prior to retinoid treatment and/or after applications of vehicle alone. Both thin sections and replicas were examined and photographed in a single-blind fashion, and the density and size distribution of gap junctions and desmosomes were computed planimetrically. Topical RA treatment induced a two-fold increase in gap junction density (P less than 0.025) over controls. In contrast, RA produced a concurrent = 35% decrease in desmosome density. Systemic CRA did not significantly alter either gap junction or desmosome density or size. Finally, neither RA nor CRA treatment appeared to influence hemidesmosome or microfilament populations. Structural changes in both treatment groups did not correlate with either tumor regression or inflammation. Topical and systemic retinoids may exert their antineoplastic activity by different cellular mechanisms.

Basal cell pseudopodia in cervical intraepithelial neoplasia; progressive reduction of number with severity: a morphometric quantification

An application of a morphometric model is used to study the stroma epithelial interface in human cervical epithelium. This model derived by Okagaki and associates estimates from two dimensional transmission electron photomicrographs the number of basal cell pseudopodia per basal cell. The investigation of the full spectrum of cervical intraepithelial neoplasia (CIN) focusing on the basal cell-stroma interface with the "multiple cell-single section" model is discussed. Significant decreases in histopathologic grades of CIN are noted in the number of pseudopodia per basal cell (N) and the ratio (F) of the area of the stems of pseudopodia to the area of the base of the basal cell.

Correlation between numbers of desmosomes and the aggressiveness of transitional cell carcinoma in human urinary bladder

Quantitative electron microscopy has been used to examine the correlation between numbers of desmosomes and the histopathological grade and stage of papillary transitional cell carcinomas in human urinary bladder. Numbers of desmosomes (desmosomal density) per 100 micrometers of cell perimeter were quantitated in 6 examples of normal epithelium, 11 noninvasive papillary transitional cell carcinomas, 8 invasive transitional cell carcinomas arising from papillary lesions, 3 invasive transitional cell carcinomas which had prominent foci of glandular and squamous differentiation, and 1 squamous cell carcinoma. Desmosomal densities were increased in noninvasive transitional cell carcinomas, as compared with normal epithelium, but decreased in invasive transitional cell carcinomas. However, in areas of glandular or squamous differentiation in invasive tumors, desmosomal densities were increased, possibly reflecting the changes in cell phenotype. The decrease in numbers of desmosomes in invasive transitional cell carcinomas may contribute to reductions in cell adhesiveness.

Endocytosis of cell-cell junctions and spontaneous cell disaggregation in a cultured human ovarian adenocarcinoma. (COLO 316)

Although cultured COLO 316 human ovarian adenocarcinoma cells are joined by extensive tight junctions and numerous demosomes in confluent monolayers, viable cells may be spontaneously released into the nutrient medium. Intracytoplasmic vesicles containing tight junctional and desmosomal elements were identified in freeze-fracture and thin section preparations of the released cells and some vesicles exhibited structural signs of degradation. Possible mechanisms for tight junctional and desmosomal interiorization and the possible relationship between junctional interiorization and certain malignant behaviors are discussed.

Cell junctions and intercellular communication

We have compared intercellular communication in normal and regenerating rat liver. Gap junctions are greatly reduced in size and numbers 29 to 35 hr after hepatectomy, but we still find some 90% of hepatocytes coupled by electrophysiological criteria. The spread of dyes such as carboxyfluorescein however is very limited in the regenerating organs as compared to the situation in the controls. We show how the apparent discrepancies between morphological and physiological data can be reconciled. We also present a summary of preliminary findings on the biosynthesis of gap junction protein and some of the conclusions one can draw from the sequence of 58 amino acids at the amino terminal of the protein.

Gap junctions in laryngeal carcinoma

The ultrastructural morphology of gap junctions in malignant keratinocytes of invasive squamous cell carcinoma of the human larynx was studied by electron microscopy. The ultrastructure of gap junctions in the malignant keratinocytes was similar to the typical intercellular gap junctions described in normal tissues. In human laryngeal carcinoma, however, the gap junctions were noticeably reduced in number as compared to normal epithelia. Spherical intracytoplasmic structures limited by gap junctional membranes were also found. These annular gap junctions arise by invagination of the cell surface membrane. The loss of gap junctions in laryngeal carcinoma is probably one of the many prerequisites which facilitate tumor invasion.

Host-tumor cellular junctions: an ultrastructural study of hepatic metastases of bronchogenic oat cell carcinoma

A light and electron microscopic study of a metastatic oat cell carcinoma of the lung in the liver of an elderly male is presented. In addition to the finding of a few desmosomes between the tumor cells, desmosomes were also found between the tumor cells and adjacent hepatocytes. The latter feature does not appear to have been reported previously in man.

A freeze-fracture study of exocytosis and reflexive gap junctions in human ovarian decidual cells

Fine-structural features of ovarian decidual cells and their mode of secretion were examined by means of freeze-fracture microscopy. Unique cortical peduncular processes contained secretory vesicles within the expanded peduncle tip, the membrane-leaflets of which exhibited a particle-poor E face adjacent to the vesicle lumen and a P face containing a greater particle number. Exocytosis from attached peduncles involved release of vesicular profiles 40-55 nm in diameter; small particles 8.5-11.5 nm in diameter were also observed at degranulation sites. In fractures revealing the E face of the plasmalemma, cytoplasmic portals at the bases of peduncular stalks were distinguishable from endocytic vesicles. The frequent occurrence of reflexive gap junctions associated with peduncles was shown by freeze-fracture. However, there appeared to be no consistent spatial relationship between gap junctions, secretory peduncles, or sites of exocytosis. Freeze-fracture analysis of the topography of reflexive gap junctional profiles revealed that such gap junctions share basic similarities with intercellular gap jum particle-free aisles. The finding in the present study of reflexive gap junctions occurring between peduncles and the cell soma, as well as between peduncles, suggests that the original definitiof the same cell should be broadened to include any gap junctional specialization formed between portions of the plasma membrane of one cell.

Epidermal intercellular relationships during carcinogenesis and cocarcinogenesis as revealed by scanning electron microscopy

Investigations with the scanning electron microscope were carried out on the skin of 80 NMRI mice after treating them with small doses of the carcinogenic substance DMBA and the cocarcinogenic agent TPA, respectively. The results were correlated with histologic, transmission electron microscope and autoradiographic observations. The epidermis of TPA-treated animals was markedly hyperplastic with an orderly arrangement of cell layers. Autoradiographically only the basal cells were heavily labelled. With the scanning and transmission electron microscope a reduced number of intercellular connections and dilatation of the intercellular spaces could be detected. After treatment with DMBA the epidermis was only moderately hyperplastic but severely dysplastic with 3H-thymidine-labelled cells in the upper layers. The most characteristic findings were the loss of the intercellular connections, especially the lateral ones, and a pronounced dilatation of the intercellular spaces. The results obtained with the scanning electron microscope were quantified using morphometrical methods.

Freeze-fracture observations on the membranes and junctions in human prostatic carcinoma and benign prostatic hypertrophy

In human prostatic carcinomatous acini, the columnar cells possessed a loosely organized meshwork of ridges and grooves and many isolated, short, and disorganized strands of tight junctions, unlike those of benign prostatic hypertrophy (BPH), where the tight junctional ridges and grooves were numerous and compact. Desmosomes were more irregular in size, shape and distribution in cancerous cells than in BPH. Our observation indicated that the junctional complexes were altered and defective in cancerous cells and probably facilitated migration of some acinar cells into the stroma. In addition, we have also shown that the membranes including the intramembranous particles of Golgi complexes, mitochondria, secretory granules and vacuoles, lipofuscin granules and nuclei, were essentially similar in cancerous and BPH columar cells.

The spread of cancer in the organism. Facts and problems

In this review, cancer is conceived as an alteration of the suface-monitored social behavior of cells. Apart from impaired growth controls, loss of residency (tissue affiliation) is the most important consequence of this homeostatic disorder. It results in local spread (penetration) which is initiated by locomotive and/or desctructive activities of the neoplastic cells. Access of cancer elements to the circulation possibly leads to distant spread (metastasis). Penetration and metastasis largely depend upon reactions of the organism, which are of an ill-understood, ambiguous nature favoring both the tumor and the host.

Trends in electron microscopy of skin

Some trends in electron microscopy of skin have emerged and should be pursued in the future. The fine structure and some basic cellular reaction patterns of epidermal cells are discussed to illustrate the interplay of morphologic, cytochemical, and tracer studies. Intracytoplasmic membranes and secretory granules, lysosomes and endocytic mechanisms, cytomembranes and cell surface specialization are discussed to show how these can be used to arrive at a more meaningful interpretation of structure. Despite all advances, however, a great deal more needs to be done before the details of skin structure are completely elucidated.

Ultrastructure and surface topography of aggregates of human limb mesenchymal cells (HLM15) in vitro

Tissue-like aggregates of human embryo fibroblasts can be created in vitro by limited aspiration of cells released from substrate during subcultivation. Aggregates increase in size, exhibit intercellular junctions, display a surface topography characteristic of cellular movement, elaborate an extracellular matrix and possess features of cellular death and phagocytosis. These cells, when introduced to a new culture environment, do not migrate away from one another as is common when a primary culture is started from tissue fragments. Instead, cells exhibit continued contact with each other, and develop complex junctional structures during that association. Cellular aggregates generated in this manner may provide a useful system for providing further information on cellular adhesion, intercellular communication, morphogenetic cell movements and the mechanisms of cell death.

Lanthanum staining of cell surface and junctional complexes in normal and malignant human oral mucosa

Biopsies from normal and malignant human oral epithelium were studied electron histochemically using lanthanum nitrate for a selective demonstration of junctional complexes at the plasma membrane of adjacent cells. The heavy metal complex was found to settle irregularly, sometimes in intimate proximity to the epithelial cell, in areas corresponding to the glycocalyx, gap junctions, desmosomes and nonspecific contact areas. Tight junctions were rarely seen. The lack of these morphological adhesive areas, the desosomal detachment seen between cancer cells and the increased lanthanum-positive cell surface may be possible factors responsible for the dissociation of oral malignant cells.